I think you're massively overestimating the amount of avgas used in aviation. It is used by the fringes of aviation only. All jets and turboprops run on Jet-A1

I think you're massively overestimating the amount of avgas used in aviation. It is used by the fringes of aviation only. All jets and turboprops run on Jet-A1 which is unleaded. All that remains is flying much less hours and using much less fuel per flight hour as well. When cars switched away from lead the impact was huge because there were so many of them using so much fuel. Avgas is really a minor thing and some airports don't even want to stock it anymore. Refineries don't like making it and as a result it's so expensive that complete engine refits with turbodiesel have become viable.